1. Field of the Invention
The present invention relates to a method of inhibiting the growth of cancer cells which are susceptible to treatment with antitumor drugs.
2. Description of the Prior Art
These days, cancer is generally treated by surgery, radiotherapy, chemotherapy (treatment with drugs), etc.
So far, chemotherapy with drugs acting directly on tumor cells to kill them has been widespread, and thus there have been many proposals as to such drugs. These drugs, however, act not only on tumor cells to kill them but also on normal cells, and thus can not produce their high therapeutic effects without being accompanied by extremely severe side effects.
Under the circumstances, attention has been drawn to drugs for enhancing immunological competence of normal cells to indirectly inhibit growth of tumor cells. Examples of such drugs are Krestin and interferon. The direct effects of such drugs on tumor cells is small but advantageous because of the low side effects.
Recently, from the viewpoint of decarcinogenesis of tumor cells (carcinogenesis is not irreversible but reversible, that is, tumor cells can be caused to approach or revert to normal cells), attention has also focused on the use of drugs capable of performing differentiation-inducing action to transform tumor cells into normal cells. These drugs have direct action on tumor cells with less side effects, and thus can be expected as promising antitumor agents which might have high therapeutic effects.
Hitherto agents have been proposed having differentiation-inductive activity, such as prostaglandin E.sub.1 which causes an increase of c-AMP. However, prostaglandin E.sub.1 is so unstable in the human body that it must be drip-infused directly to an affected site for treatment of cancer and must be used in combination with other drugs. Under the circumstances, substances having good differentiation-inductive activity and which can be effectively used as an antitumor drug with stability and low toxicity are desired.